X-ray tomography is best-suited [1] for three-dimensional anode reconstructions. This study investigates anodes removed from two consumer cells (1 Ah), namely a high-energy cell and a high-power cell.
Based on X-ray micro-CT reconstructions of the graphite anodes comprehensive sets of structural parameters are obtained. An in-depth analysis of (a) volume fractions, (b) surface areas, (c) particle size distributions and (d) tortuosity, gives insight into the different designs of the electrodes. Electrochemical impedance spectroscopy [2, 3] was performed and analyzed by the distribution of relaxation times (DRT) [4], enabling a separation of the several loss processes by their individual time constants. A transmission line model (TLM) [5] was set up assessing quantitatively the contribution of electronic and ionic transport in the porous electrode structure, as well as charge transfer and SEI resistance. Given the fact, that the effective ionic conductivity is 8 times smaller in the graphite anode of a high-energy cell, the contribution of lithium-ion transport through the electrolyte filled pores becomes significant for high currents.
References:
[1] M. Ender, J. Joos, A. Weber, E. Ivers-Tiffée, J. Power Sources 269 (2014) 912-919
[2] J. Illig, M. Ender, T. Chrobak, J.P. Schmidt, D. Klotz, E. Ivers-Tiffée, J. Electrochem. Soc. 159 (2012) A952-A960
[3] J. Illig, M. Ender, A. Weber, E. Ivers-Tiffée, J. Power Sources 282 (2015) 335-347
[4] H. Schichlein, A.C. Müller, M. Voigts, A. Krügel, E. Ivers-Tiffée, J. Appl. Electrochem. 32 (2002) 875-882
[5] J. Euler, W. Nonnenmacher, Electrochimica Acta 2 (1960) 268–286